The present invention relates to power tools; more particularly, the present invention relates to power drills in which a nose piece and drill bushing are utilized for guiding a drill bit through a drill fixture into a work piece.
In many drilling operations, particularly related to the assembly of aircraft, it is well known to utilize drilling apparatus including a nose piece with a taper lock drill bushing mounted at the outboard end. The taper lock drill bushing is used to lock the drilling apparatus to a drill fixture. The drill fixture is then positioned over a work piece. Typically, the drill fixture is rigidly mounted to the work piece to assure accurate placement of the drilled hole.
Drill fixtures include two fasteners which are used to lock the taper lock drill bushing in position against the drill fixture. The taper lock drill bushing is usually threaded into the nose piece at the end of a power drill and the nose piece is then rigidly attached to the power drill. Consequently, when the nose piece and taper lock drill bushing are attached to the power drill, the power drill is firmly affixed to the drill fixture. This allows for accurate drilling of a hole in the work piece.
A problem arises when the drilling apparatus has an outwardly extending appendage. Such outwardly extending appendage may contain operational controls, a power source or speed reduction gearing. When it is necessary to rotate the entire drilling apparatus to position the taper lock drill bushing with respect to the fasteners which extend from the drill fixture, the outwardly extending appendage may butt up against a bulk-head, a wall or a spar. Such problems most frequently occur when a hole is to be drilled near a corner. This contact of the outwardly extending appendage against the bulk-head, wall or spar prevents full rotation of the drilling apparatus and thus prevents proper engagement of the taper lock drill bushing with the fasteners which extend from the drill fixture. To solve this problem a system is required in which the nose piece may be selectively and rotatably indexed with respect to the rest of the drill apparatus while the drill apparatus is in position for drilling a hole. Such system would allow the outwardly extending appendage to not interfere with the locking of the drilling apparatus to the drill fixture.